The present invention relates to a lateral paper position correcting mechanism for use in an image forming apparatus such as a copying machine or a printer.
One known example of a conventional lateral paper position correcting mechanism is disclosed in Japanese Unexamined Patent Publication No. 7-89645. In this lateral paper position correcting mechanism, a side guide is fitted along a paper path and an oblique roller is provided beside the side guide. As the oblique roller obliquely transfers paper being fed, a side edge of the paper comes into contact with the side guide, whereby the position of the paper in the paper path is corrected in the paper's lateral direction, or in the direction perpendicular to the paper feeding direction.
In this mechanism, the oblique roller is made movable between a driving position where the oblique roller comes into contact with the paper and a retracted position where the oblique roller is separated from the paper, and a pair of transfer rollers provided immediately upstream of the oblique roller can be switched between a pressing state in which the transfer roller pair nips the paper and a non-pressing state. In paper feeding operation, the transfer rollers are set to the pressing state and feed the paper, and when a sensor senses that the leading edge of the paper has reached the location of the oblique roller, the oblique roller is set to its driving position and the transfer roller pair is set to its non-pressing state. When completion of the correction of the paper position is sensed, the oblique roller is returned to its retracted position and the transfer roller pair is set to its pressing state so that the paper is transferred downstream by the transfer roller pair thereafter.
Since the oblique roller is made movable between the driving position and the retracted position and it is returned to the retracted position upon completion of paper position correction in the aforementioned conventional lateral paper position correcting mechanism, it is possible to prevent an excessive obliquely pushing force from acting on the paper after the completion of the paper position correcting operation. Thus, this mechanism is advantageous in that the paper is less likely to be bent although it is forced in an oblique direction and brought into contact with the side guide.
There exists a potential for the once corrected paper to deviate in its lateral direction, however, because the oblique roller is moved to its retracted position immediately after the completion of the paper position correcting operation. It is therefore impossible for the aforementioned conventional mechanism to properly perform the paper position correcting operation.
The aforementioned mechanism has another drawback in that it is apt to develop a paper feeding problem since the paper is advanced only by the transfer roller pair located on the upstream side of the oblique roller after the paper position correcting operation. More specifically, there exists a frictional resistance between the side guide and the paper after the paper position correcting operation because the latter is transferred in contact with the former. Since the transfer rollers nip a rear portion of the paper (a portion closer to the trailing edge of the paper) when transferring the paper after the paper position correcting operation, a forward portion of the paper tends to jam or otherwise become stuck in the paper path due to the frictional resistance or the slope of the paper path. Thus, the mechanism needs to be improved to ensure smooth paper feeding after the paper position correcting operation.